A recent trend promotes production of ultra-concentrated formulations or systems that contain little or no water. Such formulations or concentrates are delivered to an end-use customer who then dilutes the concentrate with water to produce a final working solution. Those who use concentrates consider it an eco-friendly approach as it eliminates costs associated with shipping water and reduces material requirements for packaging. The concentrates typically include one or more nonionic surfactants because they are compatible with all other surfactant types (e.g. anionic, cationic and zwitterionic surfactants). In addition, nonionic surfactants resist precipitation with hard water and offer excellent oil grease cleaning benefits.
Household and industrial applications that employ ultra-concentrates include laundry detergents, hard surface cleaners, automatic dishwasher detergents, rinse aids, emulsification packages (such as agricultural-emulsifiers), and flotation systems (for applications such as paper de-inking and ore flotation).
Soap and detergent manufacturers use the term “diluted” to refer both to dissolution of solids and reduction of concentration of liquids. For example, liquid laundry detergent may be diluted in a tub of water. Similarly, a powdered or block laundry detergent that is dissolved in a tub of water also would be referred to as “diluted.”
A common problem for concentrated formulas that contain surfactants is formation of gels when a solid or liquid surfactant is diluted with water. For example, a formulation or concentrate consisting primarily of a 9-mole ethoxylate of nonylphenol (such as Tergitol™ NP-9) forms resilient, slow-dissolving gels when mixed with water. For end-use customers (especially household customers), these slow-dissolving gels require extensive mixing which can interfere with convenience and effectiveness of end-use or diluted formulations. One way the industry expresses a tendency of a surfactant to cause gels is a “gel range.” A typical gel range describes a percentage of samples that form gels, out of a number of samples, each having increasing surfactant concentration. For example, a gel range of less than 20% indicates that less than two samples out of nine samples form gels; the nine samples having surfactant concentrations of 10 wt. %, 20 wt. %, 30 wt. %, 40 wt. %, 50 wt. %, 60 wt. %, 70 wt. %, 80 wt. %, and 90 wt. %, each weight percentage (wt %) being based upon combined weight of surfactant and de-ionized water. A sample forms a gel when it is non-pourable for at least five seconds at 23° centigrade (° C.) when its container is inverted 180° so the container's open spout or mouth faces down. For many applications, a surfactant ideally has no gel range. In other words, it does not form gels when mixed with water.
In some cases, the tendency to form gels can be overcome by adding an anti-gelling agent such as a solvent or a polyglycol to the formulation. For example, a simple formulation containing 20 wt % of a 9-mole ethoxylate of nonylphenol (Tergitol™ NP-9) and 80 wt % propylene glycol (each wt % based on formulation weight) will not form gels upon dilution with water. However, the addition of anti-gelling agents tends to increase overall complexity and cost of the formulation, and therefore may be undesirable.
In addition to gel formation tendency, an important physical property consideration for use in selecting a surfactant is its tendency to undergo a viscosity increase as temperatures fall or decrease. Surfactant users typically select “pour point” or “pour point temperature” as a general indicator of handling characteristics of a pure surfactant under reduced temperatures. They consider pour point as that temperature below which a liquid surfactant will fail to pour from a container.
Many nonionic surfactants are alkoxylates of fatty alcohols containing greater than about eight carbons (C8+). The alkoxylates are typically block or random polymers of ethoxy, propoxy, butoxy, or even larger alkoxy groups. These alkoxylates vary in alkyl group size, usually represented by “R”, and in number of alkoxy groups in a polymer chain, also referred to as “degree of alkoxylation”. The number and size of alkoxylate groups affects surfactant performance attributes including dispersibility and stability in various solutions, detergency, foam formation, and cleaning performance.
In recent years, the global chemical industry has expressed increasing interest in using renewable resources, such as plant or seed oils, to reduce dependence on petroleum and natural gas feedstocks. Seed oils contain fatty acids that may be converted to alcohols using known technology. The alcohols, in turn, may be converted to alcohol alkoxylates by methods such as those discussed in “Nonionic Surfactants”, Martin, J. Schick, Editor, 1967, Marcel Dekker, Inc., or United States Patent Application Publication (USPAP) 2005/0170991A1. Fatty acid alcohols may also be alkoxylated using metal cyanide catalysts including (but not limited to) those described in U.S. Pat. No. 6,429,342.
Alcohols derived from natural feedstocks tend to have carbon chains that are more linear, and less branched, than alcohols derived from petroleum and natural gas products, which may be regarded as semi-linear or branched. In addition, when produced via hydrogenation of fatty acids, alcohols tend to be primary alcohols, having only one reactive group and an even number of carbon atoms in each chain or molecule. When alkoxylated, natural feedstock-derived alcohols produce surfactants that may behave somewhat differently than their petroleum and natural gas analogs. For example, alkoxylates with a generally linear structure tend to self-associate and form gels to a greater extent in water than those with a semi-linear or branched structure. As such, surfactants based upon alkoxylated, natural oil-derived alcohols often do not function as drop in replacements for surfactants based upon alkoxylated alcohols derived from petroleum and natural gas feedstocks. As they are not drop in replacements, formulators must accommodate differences between surfactants based on natural oils and surfactants based upon petroleum or natural gas in preparing formulations for various uses.
Relatively short-chain alkoxylates of linear alcohols derived from petroleum or natural gas, i.e. those where R contains from 6 to 10 carbon atoms (C6-10 or C6-C10), typically do not form gels, and are often used in applications to avoid gel formation. For example, Triton™ XL-80N, based on an alkoxylate of a C8-C10 blend of alcohols, exhibits a narrow gel range (less than 20% of the range from 0% to 100% dilution) and is often used in hard-surface formulations that require rapid dissolution in the absence of gels. Other short-chain alkoxylates that have no gel range include Plurafac™ SLF-62 (based on a C6-10 alkoxylate blend), Alfonic™ 810-60 (a C8-C10 ethoxylate), and Surfonic™ JL-80X (a C8-10 alkoxylate)
Although these relatively short-chain alkoxylates of linear alcohols form few, if any, gels upon dilution with water, they perform poorly in some applications. For example, the C8-C10alkoxylates of linear alcohols do not perform well in some standard laundry cleaning tests. Conversely, formulations with relatively long-chain alkoxylates of linear alcohols derived from petroleum or natural gas, e.g. C11-16 alcohol ethoxylates, have better detergent performance than the C8-C10 alkoxylates of linear alcohols, but tend to form more gels. Gel formation is even more of a problem for C12-18 seed-oil based alcohol ethoxylates, since these materials are 100% linear and form gels that are very difficult to dissolve in water.
One approach to improve general properties such as detergency, oil removal, or metal cleaning is to use blends of two or more nonionic surfactants. However, blends of alkoxylates, especially C10-16 alcohol alkoxylates, to give surfactants with specific properties (e.g. a certain pour point, a low or reduced gel range, and a desired detergency) when used in an ultra-concentrated formulas appear to be unknown.
U.S. Pat. No. 3,983,078 teaches the use of mixtures of long-chain alkylene oxide surfactants and short-chain alkylene oxide co-surfactants. The mixtures have a hydrophilic-lipophilic balance (HLB) in a range of from about 10.8 to 12.0. These surfactants blends are claimed as one part of complex formulations or blends that incorporate builders (sodium tripolyphosphate), hydrotropes (sodium toluene sulfonate), thickeners (sodium carboxymethyl cellulose), and other additives. In this case, “long-chain” refers to a formula: R—O—(CyH2yO)a—(CzH2zO)b—CwH2wOH, where R ranges from C8-15, a=0-11; b=0-11; a+b=4-11; y=2-3; z=2-3; w=2-3; and “short chain” encompasses a formula R1—O—(C2H4)x—C2H4OH, where R1=C8-11 and x=3.5-5. Illustrative mixtures include 60-80 wt % of the “long chain” component” and 20-40 wt % of the “short-chain” component, the weight percentages being based upon mixture weight and totaling 100 wt %.
U.S. Pat. No. 4,965,014 describes liquid nonionic surfactant mixtures having a general formula R—O—(PO)1-2(EO)6-8(H) where PO refers to propylene oxide, EO refers to ethylene oxide, O represents oxygen and H represents hydrogen. The mixtures have components with R selected so that C8=0 to 5%, C9-10=75-90%, C11-12=5-15%, C13-14=4-10%, C15-16=0 to 3%.
Patent Cooperation Treaty Publication (WO) 94/10278 describes blends of surfactants based on a mixture of component A with component B in weight ratios ranging from 4:1 to 10:1 (80 wt % to 91 wt % component A). Component A is defined as R1—(OC3H6)n-(OC2H4)p-OH, in which R1 is an alkyl residue with 6 to 10 carbon atoms, n is a number from 0.5 to 8, p is a number from 4 to 10. Component B is defined as R2—(OC2H4)q—OH, in which R2 is an alkyl residue with 10 to 22 carbon atoms and q is a number from 4 to 10. The example teaches a blend of 85% of a C8 alkoxylate with 15% of a C12-14 ethoxylate.